The proposed project is designed to systematically examine the neuropsychological processes mediating interactions between object representation and attention in Alzheimer's disease (AD). Although recent studies suggest that AD patients possess specific deficits in object-based attentional processes, it is possible that disruption of corticocortical connections within higher- order association areas may also produce pre-attentive impairment in the integration of visual information into coherent object representations. Thus, the apparent deficits exhibited by AD patients on tests of visual attention may be attributable as much to impairments in object representation as to impairments in attention per se. Identification of the ways in which object representation and attentional processes interact in AD should not only provide a better understanding of the cognitive deficits associated with this disease, but should also lead to important information about the neuropsychological substrates mediating normal object representation and attention. The proposal is divided into two sections. First, a series of classification and inspection time tasks incorporating several types of multidimensional stimuli that vary in their degree of feature integrality will be used to systematically assess differences between AD patients and normal controls in the representations mediating object perception. Second, these same stimuli will be used in a series of visual search and illusory conjunction tasks in order directly assess interactions between attentional and representional deficits in AD.